Acoustic communication in two freshwater gobies: the relationship between ambient noise, hearing thresholds and sound spectrum

Rhythmic properties of Sciaena umbra calls across space and time in the Mediterranean Sea

In animals, the rhythmical properties of calls are known to be shaped by physical constraints and the necessity of conveying information. As a consequence, investigating rhythmical properties in relation to different environmental conditions can help to shed light on the relationship between environment and species behavior from an evolutionary perspective. Sciaena umbra (fam. Sciaenidae) male fish emit reproductive calls characterized by a simple isochronous, i.e., metronome-like rhythm (the so-called R-pattern). Here, S. umbra R-pattern rhythm properties were assessed and compared between four different sites located along the Mediterranean basin (Mallorca, Venice, Trieste, Crete); furthermore, for one location, two datasets collected 10 years apart were available. Recording sites differed in habitat types, vessel density and acoustic richness; despite this, S. umbra R-calls were isochronous across all locations. A degree of variability was found only when considering the beat frequency, which was temporally stable, but spatially variable, with the beat frequency being faster in one of the sites (Venice). Statistically, the beat frequency was found to be dependent on the season (i.e. month of recording) and potentially influenced by the presence of soniferous competitors and human-generated underwater noise. Overall, the general consistency in the measured rhythmical properties (isochrony and beat frequency) suggests their nature as a fitness-related trait in the context of the S. umbra reproductive behavior and calls for further evaluation as a communicative cue.

Mating sounds in the two-spotted goby, Pomatoschistus flavescens: Effects of water temperature on acoustic featuresa)

Acoustic signals in teleost fishes play a fundamental role in reproduction. As fish are ectothermic animals, temperature has the potential to change their signal production and detection, with further implications for mating interactions. In this study, we describe the mating sounds made by the two-spotted goby, Pomatoschistus flavescens, for the first time and further investigate the effect of temperature on the acoustic features. Courtship sounds of 15 two-spotted goby males were recorded at three different temperatures: 16 °C, 19 °C, and 21 °C. As seen for other marine gobies, two-spotted goby produced two courtship sounds: drums and thumps. Drums showed similar acoustic features to other Pomatoschistus species already studied. Calling rates for both kinds of sound were not affected by the increases in temperature. However, pulse rate increased from 16 °C to 19 °C and stabilised between 19 °C and 21 °C, suggesting that two-spotted gobies reached their physiological limits at 19 °C. Spectral features were also affected by temperature, presenting higher values at 19 °C. Whether or not the observed changes in acoustic features with temperature lead to changes in mating remains to be addressed. Studies like the present one are fundamental to better comprehend how reproduction will be affected by global warming in soniferous fishes.

Toward a general model for the evolution of the auditory sensitivity under variable ambient noise conditionsa)

Ambient noise constrains the evolution of acoustic signals and hearing. An earlier fitness model showed that the trade-off between sound detection and recognition helps predict the best level of auditory sensitivity for acoustic communication in noise. Here, the early model is improved to investigate the effects of different noise masking conditions and signal-to-noise ratios (SNRs). It is revealed that low sensitivity is expected for acoustic communication over short distances in complex noisy environments provided missed sound recognition is costly. By contrast, high sensitivity is expected for acoustic communication over long distances in quieter habitats or when sounds are received with good SNRs under unfavorable noise conditions. High sensitivity is also expected in noisy environments characterized by one dominant source of noise with a fairly constant spectrum (running-water noise) or when sounds are processed using anti-masking strategies favoring the detection and recognition of sound embedded in noise. These predictions help explain unexpected findings that do not fit with the current view on the effects of environmental selection on signal and sensitivity. Model predictions are compared with those of models of signal detection in noisy conditions and results of empirical studies.

A comparison of underwater speakers for fish playback studiesa)

Acoustic playback is a key method used to determine the behavioral significance of animal sounds, including fishes. This study presents the first comparison of the acoustic quality of underwater speakers for the playback of fish sounds. Seven underwater acoustic playback systems were tested for their ability to accurately reproduce the low frequency, pulsed, courtship sounds of a small fish, Tramitichromis intermedius (Cichlidae). Results indicated that in an aquarium with low ambient noise and at low amplitude playback levels (<120 dB re 1 μPa), the Clark Synthesis speakers were the best choice for playback at moderate distances (>20 cm), and that the Electro-Voice UW30 was the best speaker for short distance (<20 cm) playback of low frequency fish sounds. However, in aquaria with higher levels of ambient noise and at higher amplitude playback levels, the Clark Synthesis speakers performed best. However, none of these speaker systems reproduced a high-fidelity quality fish sound. It is important when using underwater speakers for behavioral studies that there is a careful assessment of the played back sound and comparison to the original sound.

Correlation between acoustic divergence and phylogenetic distance in soniferous European gobiids (Gobiidae; Gobius lineage)

In fish, species identity can be encoded by sounds, which have been thoroughly investigated in European gobiids (Gobiidae, Gobius lineage). Recent evolutionary studies suggest that deterministic and/or stochastic forces could generate acoustic differences among related animal species, though this has not been investigated in any teleost group to date. In the present comparative study, we analysed the sounds from nine soniferous gobiids and quantitatively assessed their acoustic variability. Our interspecific acoustic study, incorporating for the first time the representative acoustic signals from the majority of soniferous gobiids, suggested that their sounds are truly species-specific (92% of sounds correctly classified into exact species) and each taxon possesses a unique set of spectro-temporal variables. In addition, we reconstructed phylogenetic relationships from a concatenated molecular dataset consisting of multiple molecular markers to track the evolution of acoustic signals in soniferous gobiids. The results of this study indicated that the genus Padogobius is polyphyletic, since P. nigricans was nested within the Ponto-Caspian clade, while the congeneric P. bonelli turned out to be a sister taxon to the remaining investigated soniferous species. Lastly, by extracting the acoustic and genetic distance matrices, sound variability and genetic distance were correlated for the first time to assess whether sound evolution follows a similar phylogenetic pattern. The positive correlation between the sound variability and genetic distance obtained here emphasizes that certain acoustic features from representative sounds could carry the phylogenetic signal in soniferous gobiids. Our study was the first attempt to evaluate the mutual relationship between acoustic variation and genetic divergence in any teleost fish.

Fish sounds and boat noise are prominent soundscape contributors in an urban European estuary

Passive acoustic monitoring is a valuable tool for non-intrusive monitoring of marine environments, also allowing the assessment of underwater noise that can negatively affect marine organisms. Here we provide for the first time, an assessment of noise levels and temporal soundscape patterns for a European estuary. We used several eco-acoustics methodologies to characterize the data collected over six weeks within May 2016 - July 2017 from Tagus estuary. Biophony was the major contributor dominated by fish vocalizations and the main driver for seasonal patterns. Maritime traffic was the major source of anthropogenic noise, with daily patterns monitored using 1584 Hz third-octave band level. This indicator avoided biophony and geophony, unlike other indicators proposed for the EU Marine Strategy Framework Directive. Furthermore, the frequency overlap between anthropophony and biophony demands precautionary actions and calls for further research. This study provides an assessment that will be useful for future monitoring and management strategies.

Acoustic particle motion detection in the snapping shrimp (Alpheus richardsoni)

Many crustaceans produce sounds that might be used in communication. However, little is known about sound detection in crustaceans, hindering our understanding of crustacean acoustic communication. Sound detection has been determined only for a few species, and for many species, it is unclear how sound is perceived: as particle motion or sound pressure. Snapping shrimp are amongst the loudest and most pervasive marine sound sources. They produce snaps during interactions with conspecifics, and they also interact with soniferous heterospecifics. If they can hear, then sound could facilitate key behavioral interactions. We measured the auditory sensitivity of the snapping shrimp, Alpheus richardsoni, using auditory evoked potentials in response to a shaker table that generated only particle motion and an underwater speaker that generated both particle motion and sound pressure. Auditory detection was most sensitive between 80 and 100 Hz, and auditory evoked potentials were detected up to 1500 Hz. Snapping shrimp responded to both the shaker table and the underwater speaker, demonstrating that they detect acoustic particle motion. Crushing the statocyst reduced or eliminated hearing sensitivity. We conclude that snapping shrimp detect acoustic particle motion using the statocyst, they might detect conspecifics and heterospecifics, and hearing could facilitate key behavioral interactions.

Assessing auditory masking for management of underwater anthropogenic noise

Masking is often assessed by quantifying changes, due to increasing noise, to an animal's communication or listening range. While the methods used to measure communication or listening ranges are functionally similar if used for vocalizations, they differ in their approaches: communication range is focused on the sender's call, while the listening range is centered on the listener's ability to perceive any signal. How these two methods differ in their use and output is important for management recommendations. Therefore it was investigated how these two methods may alter the conclusions of masking assessments based on Atlantic cod calls in the presence of a commercial air gun array. The two methods diverged with increasing distance from the masking noise source with maximum effects lasting longer between air gun pulses in terms of communication range than listening range. Reductions in the cod's communication ranges were sensitive to fluctuations in the call's source level. That instability was not observed for the listening range. Overall, changes to the cod's communication range were more conservative but very sensitive to the call source level. A high level of confidence in the call is therefore required, while confidence in the receiver's audiogram and soundscape is required for the listening range method.

Ecology of sound communication in fishes

Fishes communicate acoustically under ecological constraints which may modify or hinder signal transmission and detection and may also be risky. This makes it important to know if and to what degree fishes can modify acoustic signalling when key ecological factors-predation pressure, noise and ambient temperature-vary. This paper reviews short-time effects of the first two factors; the third has been reviewed recently (Ladich, 2018). Numerous studies have investigated the effects of predators on fish behaviour, but only a few report changes in calling activity when hearing predator calls as demonstrated when fish responded to played-back dolphin sounds. Furthermore, swimming sounds of schooling fish may affect predators. Our knowledge on adaptations to natural changes in ambient noise, for example caused by wind or migration between quiet and noisier habitats, is limited. Hearing abilities decrease when ambient noise levels increase (termed masking), in particular in taxa possessing enhanced hearing abilities. High natural and anthropogenic noise regimes, for example vessel noise, alter calling activity in the field and laboratory. Increases in sound pressure levels (Lombard effect) and altered temporal call patterns were also observed, but no switches to higher sound frequencies. In summary, effects of predator calls and noise on sound communication are described in fishes, yet sparsely in contrast to songbirds or whales. Major gaps in our knowledge on potential negative effects of noise on acoustic communication call for more detailed investigation because fishes are keystone species in many aquatic habitats and constitute a major source of protein for humans.

Acoustic communication in marine shallow waters: testing the acoustic adaptive hypothesis in sand gobies

Acoustic communication is an important part of social behaviour of fish species that live or breed in shallow noisy waters. Previous studies have shown that some fish species exploit a quiet window in the background noise for communication. However, it remains to be examined whether hearing abilities and sound production of fish are adapted to marine habitats presenting high hydrodynamism. Here, we investigated whether the communication system of the painted (Pomatoschistus pictus) and the marbled (Pomatoschistus marmoratus) gobies is adapted to enhance sound transmission and reception in Atlantic shallow water environments. We recorded and measured the sound pressure levels of social vocalisations of both species, as well as snapshots of ambient noise of habitats characterised by different hydrodynamics. Hearing thresholds (in terms of both sound pressure and particle acceleration) and responses to conspecific signals were determined using the auditory evoked potential recording technique. We found that the peak frequency range (100-300 Hz) of acoustic signals matched the best hearing sensitivity in both species and appeared well adapted for short-range communication in Atlantic habitats. Sandy/rocky exposed beaches presented a quiet window, observable even during the breaking of moderate waves, coincident with the main sound frequencies and best hearing sensitivities of both species. Our data demonstrate that the hearing abilities of these gobies are well suited to detect conspecific sounds within typical interacting distances (a few body lengths) in Atlantic shallow waters. These findings lend support to the acoustic adaptive hypothesis, under the sensory drive framework, proposing that signals and perception systems coevolve to be effective within local environment constraints.

Identifying sagittal otoliths of Mediterranean Sea gobies: variability among phylogenetic lineages

In this study, we describe and analyse the morphology of the sagitta, the largest otolith, of 25 species of Gobiidae inhabiting the Adriatic and north-western Mediterranean seas. Our goal was to test the usefulness and efficiency of sagittal otoliths for species identification. Our analysis of otolith contours was based on mathematical descriptors called wavelets, which are related to multi-scale decompositions of contours. Two methods of classification were used: an iterative system based on 10 wavelets that searches the Anàlisi de Formes d'Otòlits (AFORO) database and a discriminant method based only on the fifth wavelet. With the exception of paedomorphic species, the results showed that otolith anatomy and morphometry can be used as diagnostic characters distinguishing the three Mediterranean phylogenetic goby lineages (Pomatoschistus or sand-goby lineage, Aphia lineage and Gobius lineage). The main anatomical differences were related to overall shape (square to rhomboid), the development and shape of the postero-dorsal and antero-ventral lobes and the degree of convexity of dorsal and ventral margins. Iterative classifications and discriminant analysis of otolith contour provided very similar results. In both cases, more than 70% of specimens were correctly classified to species and more than 80% to genus. Iterations in the larger AFORO database (including 216 families of teleosts) attained a 100% correct classification at the family level.

Use of baited remote underwater video (BRUV) and motion analysis for studying the impacts of underwater noise upon free ranging fish and implications for marine energy management

Free-ranging individual fish were observed using a baited remote underwater video (BRUV) system during sound playback experiments. This paper reports on test trials exploring BRUV design parameters, image analysis and practical experimental designs. Three marine species were exposed to playback noise, provided as examples of behavioural responses to impulsive sound at 163-171dB re 1μPa (peak-to-peak SPL) and continuous sound of 142.7dB re 1μPa (RMS, SPL), exhibiting directional changes and accelerations. The methods described here indicate the efficacy of BRUV to examine behaviour of free-ranging species to noise playback, rather than using confinement. Given the increasing concern about the effects of water-borne noise, for example its inclusion within the EU Marine Strategy Framework Directive, and the lack of empirical evidence in setting thresholds, this paper discusses the use of BRUV, and short term behavioural changes, in supporting population level marine noise management.

The relationship between acoustic habitat, hearing and tonal vocalizations in the Antillean manatee (Trichechus manatus manatus, Linnaeus, 1758)

The Antillean manatee (Trichechus manatus manatus) is an endangered marine mammal that inhabits the Caribbean Sea and riverine systems in Central America. Their acoustic behavior is relevant for individual identification, mating and parental care. Manatees produce tonal sounds with highest energy in the second harmonic (usually 5 kHz), and their audiogram indicates sensitivity from 0.3 kHz to 90 kHz with lowest thresholds in the 16 to 18 kHz range. We recorded manatees in the San San River, a highly polluted riverine system in Panama, using a stereo array. Frequency transmission experiments were conducted in four subhabitats, categorized using riverine vegetation. Incidental interactions of manatees and small motorboats were examined. Acoustic transmission was linearly related to tonal vocalization characters: correlations were stronger in freshwater than in transition and marine environments. Two bands, 0.6 to 2 kHz and 3 to 8 kHz, attenuate similarly in all subhabitats, and these bands encompass F₀ (tone) and peak frequency respectively of manatee tonal calls. Based on our data we conclude that frequency transmission depends mainly on river depth and bottom characteristics, also motorboat sounds mask signals from 3.5 kHz to 8 kHz, which overlaps the peak frequency of tonal calls. In spite of differences between acoustic transmission in subhabitats of the San San River, manatees utilize bands that transmit efficiently in all subhabitats.

Sound pressure enhances the hearing sensitivity of Chaetodon butterflyfishes on noisy coral reefs

Butterflyfishes are conspicuous members of coral reefs that communicate with acoustic signals during social interactions with mates and other conspecifics. Members of the genus Chaetodon have a laterophysic connection (LC), a unique association of anterior swim bladder horns and the cranial lateral line, but the action of the LC system on auditory sensitivity was previously unexplored. Baseline auditory evoked potential threshold experiments show that Forcipiger flavissimus (which lacks swim bladder horns and LC) is sensitive to sound tones from 100 Hz up to 1000 Hz, and that thresholds for three species of Chaetodon were 10-15 dB lower with extended hearing ranges up to 1700-2000 Hz. The relatively high thresholds to sound pressure and low pass response near 500 Hz for all four species is consistent with a primary sensitivity to hydrodynamic particle acceleration rather than sound pressure. Deflation of the swim bladder in Forcipiger had no measurable effect on auditory sensitivity. In contrast, displacement of gas from the swim bladder horns in C. multicinctus and C. auriga increased thresholds (decreased sensitivity) by approximately 10 dB with the greatest effect at 600 Hz. The evolution of swim bladder horns associated with the LC system in Chaetodon has increased hearing sensitivity through sound pressure transduction in the frequency bands used for social acoustic communication. The close affiliative behaviors that are common in Chaetodon and other butterflyfish species facilitate sound perception and acoustic communication at close distances relative to the high background noise levels found in their natural reef environment.

Acoustics of fish shelters: background noise and signal-to-noise ratio

Fish shelters (flat stones, shells, artificial covers, etc., with a hollow beneath) increase the sound pressure levels of low frequency sounds (<150 Hz) outside the nest cavity, see Lugli [(2012). J. Acoust. Soc. Am. 132, 3512-3524]. Since some calling males only produce sound when a female is inside the shelter, this study examines the effect of sound amplification by the shelter on signal-to-noise ratio (SNR) in the nest. Background noise amplification by the shelter was examined under both laboratory (stones and shells) and field (stones) conditions, and the SNR of tones inside the nest cavity was measured by performing acoustic tests on stones in the stream. Stone and shell shelters amplify the background noise pressure levels inside the cavity with comparable gains and at similar frequencies of an active sound source. Inside the cavity of stream stones, the mean SNR of tones increased significantly below 125 Hz and peaked at 65 Hz (+10 dB). Implications for fish acoustic communication inside nest enclosures are discussed.

Auditory brainstem responses in Cope's gray treefrog (Hyla chrysoscelis): effects of frequency, level, sex and size

Our knowledge of the hearing abilities of frogs and toads is largely defined by work with a few well-studied species. One way to further advance comparative work on anuran hearing would be greater use of minimally invasive electrophysiological measures, such as the auditory brainstem response (ABR). This study used the ABR evoked by tones and clicks to investigate hearing in Cope's gray treefrog (Hyla chrysoscelis). The objectives were to characterize the effects of sound frequency, sound pressure level, and subject sex and body size on ABRs. The ABR in gray treefrogs bore striking resemblance to ABRs measured in other animals. As stimulus level increased, ABR amplitude increased and latency decreased, and for responses to tones, these effects depended on stimulus frequency. Frequency-dependent differences in ABRs were correlated with expected differences in the tuning of two sensory end organs in the anuran inner ear (the amphibian and basilar papillae). The ABR audiogram indicated two frequency regions of increased sensitivity corresponding to the expected tuning of the two papillae. Overall, there was no effect of subject size and only small effects related to subject sex. Together, these results indicate the ABR is an effective method to study audition in anurans.

Sound production mechanism in Gobius paganellus (Gobiidae)

Gobiidae, the largest fish family (&gt;1500 species), has species from at least 10 genera that produce sounds for communication. Studies focused on goby sound production mechanisms have suggested that sounds are produced by the forcible ejection of water through small apertures in the opercles (hydrodynamic mechanism). The present study was a multidisciplinary investigation (morphology, muscle histology, high-speed video, sound analysis and electromyography) of the sound emission mechanism in Gobius paganellus, which produces both pulsed and tonal calls. Two populations were used, from Brittany and Venice. In the French population, sounds were accompanied by a suite of coordinated movements of the buccal, branchial and opercular regions. This was not the case in the Venetian population, and thus the direct role of head movements in sound production was rejected. The hydrodynamic mechanism hypothesis was also rejected in G. paganellus on the basis of sound oscillogram shape and because sounds are still produced after the opercles and hyohyoid muscles are cut. The use of both electromyography and electron microscopy showed that the levator pectoralis muscle, which originates on the skull and inserts on the dorsal tip of the cleithrum, is involved in sound production. We propose that the contraction of this muscle and associated vibration of the large radials is used to make sounds. In addition, we propose that different sound types (pulsed sounds and tonal calls) could occur because of differences in fish size.

Evidence for hearing loss in amblyopsid cavefishes

The constant darkness of caves and other subterranean habitats imposes sensory constraints that offer a unique opportunity to examine evolution of sensory modalities. Hearing in cavefishes has not been well explored, and here we show that cavefishes in the family Amblyopsidae are not only blind but have also lost a significant portion of their hearing range. Our results showed that cave and surface amblyopsids shared the same audiogram profile at low frequencies but only surface amblyopsids were able to hear frequencies higher than 800 Hz and up to 2 kHz. We measured ambient noise in aquatic cave and surface habitats and found high intensity peaks near 1 kHz for streams underground, suggesting no adaptive advantage in hearing in those frequencies. In addition, cave amblyopsids had lower hair cell densities compared with their surface relative. These traits may have evolved in response to the loud high-frequency background noise found in subterranean pools and streams. This study represents the first report of auditory regression in a subterranean organism.

Hearing in cichlid fishes under noise conditions

Background

Hearing thresholds of fishes are typically acquired under laboratory conditions. This does not reflect the situation in natural habitats, where ambient noise may mask their hearing sensitivities. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels. This enabled us to determine whether species with and without hearing specializations are differently affected by noise.

Methodology/Principal Findings

We investigated auditory sensitivities in the orange chromide Etroplus maculatus, which possesses anterior swim bladder extensions, and the slender lionhead cichlid Steatocranus tinanti, in which the swim bladder is much smaller and lacks extensions. E. maculatus was tested between 0.2 and 3kHz and S. tinanti between 0.1 and 0.5 kHz using the auditory evoked potential (AEP) recording technique. In both species, SPL and PAL audiograms were determined in the presence of quiet laboratory conditions (baseline) and continuous white noise of 110 and 130 dB RMS. Baseline thresholds showed greatest hearing sensitivity around 0.5 kHz (SPL) and 0.2 kHz (PAL) in E. maculatus and 0.2 kHz in S. tinanti. White noise of 110 dB elevated the thresholds by 0–11 dB (SPL) and 7–11 dB (PAL) in E. maculatus and by 1–2 dB (SPL) and by 1–4 dB (PAL) in S. tinanti. White noise of 130 dB elevated hearing thresholds by 13–29 dB (SPL) and 26–32 dB (PAL) in E. maculatus and 6–16 dB (SPL) and 6–19 dB (PAL) in S. tinanti.

Conclusions

Our data showed for the first time for SPL and PAL thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected. This indicates that noise can limit sound detection and acoustic orientation differently within a single fish family.

Auditory evoked potential audiometry in fish

A recent survey lists more than 100 papers utilizing the auditory evoked potential (AEP) recording technique for studying hearing in fishes. More than 95 % of these AEP-studies were published after Kenyon et al. introduced a non-invasive electrophysiological approach in 1998 allowing rapid evaluation of hearing and repeated testing of animals. First, our review compares AEP hearing thresholds to behaviorally gained thresholds. Second, baseline hearing abilities are described and compared in 111 fish species out of 51 families. Following this, studies investigating the functional significance of various accessory hearing structures (Weberian ossicles, swim bladder, otic bladders) by eliminating these morphological structures in various ways are dealt with. Furthermore, studies on the ontogenetic development of hearing are summarized. The AEP-technique was frequently used to study the effects of high sound/noise levels on hearing in particular by measuring the temporary threshold shifts after exposure to various noise types (white noise, pure tones and anthropogenic noises). In addition, the hearing thresholds were determined in the presence of noise (white, ambient, ship noise) in several studies, a phenomenon termed masking. Various ecological (e.g., temperature, cave dwelling), genetic (e.g., albinism), methodical (e.g., ototoxic drugs, threshold criteria, speaker choice) and behavioral (e.g., dominance, reproductive status) factors potentially influencing hearing were investigated. Finally, the technique was successfully utilized to study acoustic communication by comparing hearing curves with sound spectra either under quiet conditions or in the presence of noise, by analyzing the temporal resolution ability of the auditory system and the detection of temporal, spectral and amplitude characteristics of conspecific vocalizations.

Acoustics of fish shelters: frequency response and gain properties

Many teleosts emit sounds from cavities beneath stones and other types of submerged objects, yet the acoustical properties of fish shelters are virtually unexplored. This study examines the gain properties of shelters commonly used by Mediterranean gobies as hiding places and/or nest sites in the field (flat stones, shells belonging to five bivalve species), or within aquarium tanks (tunnel-shaped plastic covers, concrete blocks, concrete cylinder pipe, halves of terracotta flower pots). All shelters were acoustically stimulated using a small underwater buzzer, placed inside or around the shelter to mimic a fish calling from the nest site, and different types of driving stimuli (white noise, pure tones, and artificial pulse trains). Results showed the presence of significant amplitude gain (3-18 dB) at frequencies in the range 100-150 Hz in all types of natural shelters but one (Mytilus), terracotta flower pots, and concrete blocks. Gain was higher for stones and artificial shelters than for shells. Gain peak amplitude increased with the weight of stones and shells. Conclusions were verified by performing analogous acoustical tests on flat stones in the stream. Results draw attention to the use of suitable shelters for proper recording of sounds produced by fishes kept within laboratory aquaria.

Relationship between swim bladder morphology and hearing abilities--a case study on Asian and African cichlids

Background

Several teleost species have evolved anterior extensions of the swim bladder which come close to or directly contact the inner ears. A few comparative studies have shown that these morphological specializations may enhance hearing abilities. This study investigates the diversity of swim bladder morphology in four Asian and African cichlid species and analyzes how this diversity affects their hearing sensitivity.

Methodology/Principal Findings

We studied swim bladder morphology by dissections and by making 3D reconstructions from high-resolution microCT scans. The auditory sensitivity was determined in terms of sound pressure levels (SPL) and particle acceleration levels (PAL) using the auditory evoked potential (AEP) recording technique. The swim bladders in Hemichromis guttatus and Steatocranus tinanti lacked anterior extensions and the swim bladder was considerably small in the latter species. In contrast, Paratilapia polleni and especially Etroplus maculatus possessed anterior extensions bringing the swim bladder close to the inner ears. All species were able to detect frequencies up to 3 kHz (SPL) except S. tinanti which only responded to frequencies up to 0.7 kHz. P. polleni and E. maculatus showed significantly higher auditory sensitivities at 0.5 and 1 kHz than the two species lacking anterior swim bladder extensions. The highest auditory sensitivities were found in E. maculatus, which possessed the most intimate swim bladder-inner ear relationship (maximum sensitivity 66 dB re 1 µPa at 0.5 kHz).

Conclusions

Our results indicate that anterior swim bladder extensions seem to improve mean absolute auditory sensitivities by 21–42 dB (SPLs) and 21–36 dB (PALs) between 0.5 and 1 kHz. Besides anterior extensions, the size of the swim bladder appears to be an important factor for extending the detectable frequency range (up to 3 kHz).

The effect of stimulus type and background noise on hearing abilities of the round goby Neogobius melanostomus

The auditory abilities of the round goby Neogobius melanostomus were quantified using auditory evoked potential recordings, using tone bursts and conspecific call stimuli. Fish were tested over a range of sizes to assess effects of growth on hearing ability. Tests were also run with and without background noise to assess the potential effects of masking in a natural setting. Neogobius melanostomus detected tone bursts from 100 to 600 Hz with no clear best frequency in the pressure domain but were most sensitive to 100 Hz tone stimuli when examined in terms of particle acceleration. Responses to a portion of the N. melanostomus call occurred at a significantly lower threshold than responses to pure tone stimulation. There was no effect of size on N. melanostomus hearing ability, perhaps due to growth of the otolith keeping pace with growth of the auditory epithelium. Neogobius melanostomus were masked by both ambient noise and white noise, but not until sound pressure levels were relatively high, having a 5-10 dB threshold shift at noise levels of 150 dB re 1 µPa and higher but not at lower noise levels.

Year-round variability of ambient noise in temperate freshwater habitats and its implications for fishes

Changes in habitat acoustics over the year can potentially affect fish hearing and orientation to sound, especially in temperate climates. This is the first study where year-round changes in ambient noise in aquatic habitats were assessed. Seven different European fresh-water habitats were chosen for this study. Sound pressure level (SPL) and spectral composition of the ambient noise varied in both quiet stagnant habitats (lakes, backwaters) and in flowing habitats (streams, rivers). Linear equivalent SPL (L(Leq, 60s)) tended to be lower in stagnant habitats (means: 91.6-111.7 dB) than in flowing habitats (means: 111.2-133.4 dB). The changes in SPL were smallest in the river (means: 4.2-4.4 dB, maxima: 8.5-10.1 dB), whereas significantly higher values were measured in stagnant habitats and the stream (means: 9.9-14.9 dB, maxima: 25.1-30.9 dB). The spectral compositions of the ambient noise determined at different times of the year were highly correlated to each other at the river sites (mean cross-correlation coefficients: 0.85 and 0.94) and were weaker or not correlated at the other study sites (means: 0.24-0.76). The changes in ambient noise spectra were negatively correlated to changes in SPL, indicating that large changes in SPLs were accompanied by large changes in spectral composition and vice versa. Comparison of these ecoacoustical data with a preceding study (Amoser and Ladich in J Exp Biol 208:3533-3542, 2005) indicates that the auditory sensitivity in hearing specialists is affected by changes in ambient noise levels and spectra throughout a year and that this effect tends to be more pronounced in stagnant waters and the stream than at river sites. On the other hand, absolute noise levels result in a higher degree of masking in flowing waters.

Sound pressure and particle acceleration audiograms in three marine fish species from the Adriatic Sea

Fishes show great variability in hearing sensitivity, bandwidth, and the appropriate stimulus component for the inner ear (particle motion or pressure). Here, hearing sensitivities in three vocal marine species belonging to different families were described in terms of sound pressure and particle acceleration. In particular, hearing sensitivity to tone bursts of varying frequencies were measured in the red-mouthed goby Gobius cruentatus, the Mediterranean damselfish Chromis chromis, and the brown meagre Sciaena umbra using the non-invasive auditory evoked potential-recording technique. Hearing thresholds were measured in terms of sound pressure level and particle acceleration level in the three Cartesian directions using a newly developed miniature pressure-acceleration sensor. The brown meagre showed the broadest hearing range (up to 3000 Hz) and the best hearing sensitivity, both in terms of sound pressure and particle acceleration. The red-mouthed goby and the damselfish were less sensitive, with upper frequency limits of 700 and 600 Hz, respectively. The low auditory thresholds and the large hearing bandwidth of S. umbra indicate that sound pressure may play a role in S. umbra's hearing, even though pronounced connections between the swim bladder and the inner ears are lacking.

The acoustics and acoustic behavior of the California spiny lobster (Panulirus interruptus)

Numerous animals produce sounds during interactions with potential predators, yet little is known about the acoustics of these sounds, especially in marine environments. California spiny lobsters (Panulirus interruptus) produce pulsatile rasps when interacting with potential predators. They generate sound using frictional structures located at the base of each antenna. This study probes three issues--the effect of body size on signal features, behavioral modification of sound features, and the influence of the ambient environment on the signal. Body size and file length were positively correlated, and larger animals produced lower pulse rate rasps. Ambient noise levels (149.3 dB re 1 microPa) acoustically obscured many rasps (150.4+/-2.0 dB re 1 microPa) at distances from 0.9-1.4 m. Significantly higher numbers of pulses, pulse rate, and rasp duration were produced in rasps generated with two antennae compared to rasps produced with only one antenna. Strong periodic resonances were measured in tank-recorded rasps, whereas field-recorded rasps had little frequency structure. Spiny lobster rasps exhibit flexibility in acoustic signal features, but their propagation is constrained, perhaps beneficially, by the noisy marine environment. Examining the connections between behavior, environment, and acoustics is critical for understanding this fundamental type of animal communication.

Acoustic pressure and particle motion thresholds in six sciaenid fishes

Sciaenid fishes are important models of fish sound production, but investigations into their auditory abilities are limited to acoustic pressure measurements on five species. In this study, we used auditory brainstem response (ABR) to assess the pressure and particle acceleration thresholds of six sciaenid fishes commonly found in Chesapeake Bay, eastern USA: weakfish(Cynoscion regalis), spotted seatrout (Cynoscion nebulosus),Atlantic croaker (Micropogonias undulatus), red drum (Sciaenops ocellatus), spot (Leiostomus xanthurus) and northern kingfish(Menticirrhus saxatilis). Experimental subjects were presented with pure 10 ms tone bursts in 100 Hz steps from 100 Hz to 1.2 kHz using an airborne speaker. Sound stimuli, monitored with a hydrophone and geophone,contained both pressure and particle motion components. Sound pressure and particle acceleration thresholds varied significantly among species and between frequencies; audiograms were notably flatter for acceleration than pressure at low frequencies. Thresholds of species with diverticulae projecting anteriorly from their swim bladders (weakfish, spotted seatrout,and Atlantic croaker) were typically but not significantly lower than those of species lacking such projections (red drum, spot, northern kingfish). Sciaenids were most sensitive at low frequencies that overlap the peak frequencies of their vocalizations. Auditory thresholds of these species were used to estimate idealized propagation distances of sciaenid vocalizations in coastal and estuarine environments.

Development of vocalization, auditory sensitivity and acoustic communication in the Lusitanian toadfish Halobatrachus didactylus

The ontogenetic development of acoustic communication has so far only been investigated in one fish species. In order to determine whether detectability of conspecific sounds changes during growth in a species with limited hearing abilities (generalist), we investigated the development of auditory sensitivity and agonistic vocalizations in the Lusitanian toadfish Halobatrachus didactylus. Agonistic grunts were recorded, their sound pressure levels determined, and auditory sensitivities measured in five different size groups ranging from 3 to 32 cm standard length. Hearing thresholds were obtained using the auditory evoked potentials (AEP) recording technique. Dominant frequency, sound duration and number of pulses decreased,whereas pulse period and sound level increased with increasing fish size. The best hearing was below 300 Hz in all groups. Lower hearing sensitivity was found in the smallest juveniles at 100 Hz as well as at higher frequencies(800 and 1000 Hz). Comparisons between audiograms and sound spectra within the same-sized fish revealed that smaller juveniles would be barely able to detect agonistic grunts, while these vocalizations were clearly perceived by larger fish. In the latter, the main energy of sounds was found at the most sensitive frequencies. This study demonstrates that acoustic communication in the Lusitanian toadfish might be absent in early developmental stages and seems to start when juveniles are able to generate grunts of higher sound level and lower dominant frequency.

Sound production and spectral hearing sensitivity in the Hawaiian sergeant damselfish, Abudefduf abdominalis

Sounds provide important signals for inter- and intraspecific communication in fishes, but few studies examine fish acoustic behavior in the context of coevolution of sound production and hearing ability within a species. This study characterizes the acoustic behavior in a reproductive population of the Hawaiian sergeant fish, Abudefduf abdominalis, and compares acoustic features to hearing ability, measured by the auditory evoked potential (AEP)technique. Sergeant fish produce sounds at close distances to the intended receiver (⩽1–2 body lengths), with different pulse characteristics that are associated primarily with aggression, nest preparation and courtship–female-visit behaviors. Energy peaks of all sounds were between 90 and 380 Hz, whereas courtship–visit sounds had a pulse repetition rate of 125 Hz with harmonic intervals up to 1 kHz. AEP threshold,which is probably higher than the behavioral threshold, indicates best sensitivity at low frequencies (95–240 Hz), with the lowest threshold at 125 Hz (123–127 dBrms re: 1 μPa). Thus, sound production and hearing in A. abdominalis are closely matched in the frequency domain and are useful for courtship and mating at close distances. Measured hearing thresholds did not differ among males and females during spawning or non-spawning periods, which indicates a lack of sex differences and seasonal variation in hearing capabilities. These data provide the first evidence that Abudefduf uses true acoustic communication on a level similar to that of both more derived (e.g. Dascyllus, Chromis) and more basal (e.g. Stegastes) soniferous pomacentrids. This correlation between sound production and hearing ability is consistent with the sensory drive model of signal evolution in which the sender and receiver systems coevolve within the constraints of the environment to maximize information transfer of acoustic signals.

Stream ambient noise, spectrum and propagation of sounds in the goby Padogobius martensii: sound pressure and particle velocity

The most sensitive hearing and peak frequencies of courtship calls of the stream goby, Padogobius martensii, fall within a quiet window at around 100 Hz in the ambient noise spectrum. Acoustic pressure was previously measured although Padogobius likely responds to particle motion. In this study a combination pressure (p) and particle velocity (u) detector was utilized to describe ambient noise of the habitat, the characteristics of the goby's sounds and their attenuation with distance. The ambient noise (AN) spectrum is generally similar for p and u (including the quiet window at noisy locations), although the energy distribution of u spectrum is shifted up by 50-100 Hz. The energy distribution of the goby's sounds is similar for p and u spectra of the Tonal sound, whereas the pulse-train sound exhibits larger p-u differences. Transmission loss was high for sound p and u: energy decays 6-10 dB10 cm, and sound pu ratio does not change with distance from the source in the nearfield. The measurement of particle velocity of stream AN and P. martensii sounds indicates that this species is well adapted to communicate acoustically in a complex noisy shallow-water environment.

Preceding weak noise sharpens the frequency tuning and elevates the response threshold of the mouse inferior collicular neurons through GABAergic inhibition

In acoustic communication, animals must extract biologically relevant signals that are embedded in noisy environment. The present study examines how weak noise may affect the auditory sensitivity of neurons in the central nucleus of the mouse inferior colliculus (IC) which receives convergent excitatory and inhibitory inputs from both lower and higher auditory centers. Specifically, we studied the frequency sensitivity and minimum threshold of IC neurons using a pure tone probe and a weak white noise masker under forward masking paradigm. For most IC neurons, probe-elicited response was decreased by a weak white noise that was presented at a specific gap (i.e. time window). When presented within this time window, weak noise masking sharpened the frequency tuning curve and increased the minimum threshold of IC neurons. The degree of weak noise masking of these two measurements increased with noise duration. Sharpening of the frequency tuning curve and increasing of the minimum threshold of IC neurons during weak noise masking were mostly mediated through GABAergic inhibition. In addition, sharpening of frequency tuning curve by the weak noise masker was more effective at the high than at low frequency limb. These data indicate that in the real world the ambient noise may improve frequency sensitivity of IC neurons through GABAergic inhibition while inevitably decrease the frequency response range and sensitivity of IC neurons.